Pope John Paul II has opened a worldwide synod of bishops to address such questions as how to attract candidates to the priesthood without abandoning rules demanding that priests be celibate and forsake marriage.

The monthlong synod on the priesthood is to focus on the problem of "burnout" among the church's "shepherds," challenges to celibacy and a shrinking number of interested candidates.The pontiff inaugurated the assembly on Sunday by celebrating a solemn Mass in St. Peter's Basilica for some 1,000 priests, bishops and cardinals from around the world.

The synod, an advisory body that meets to discuss major issues in the Roman Catholic Church, was called by John Paul to discuss the formation of priests.

"Let me express the hope that your labors here will produce the abundant fruit which the ecclesiastical community is expecting," the pope, clad in gold robes and miter, said in his homily.

He noted that bishops from China, Vietnam and Laos were missing from the gathering and said he hoped they would join the synod later.

No reason was given for the absence of bishops Jean Khamse of Laos and Cambodia, Paul Nguyen Van Hoa and Emmanuel Le Phong Thuan of Vietnam, and Lucas Liu Hsien-Tang of China. The Vatican says the church faces serious restrictions in those communist countries.

At the last synod in 1987, dealing with the laity, Vietnamese prelates arrived midway through the assembly.

The synod is expected to focus on the difficulty in maintaining the church's rules "in a world characterized by eroticism," as a working document put it. The rules themselves are not expected to be subjects for debate, however, as the pope has shown no indication they might be changed.

Several sexual scandals have embarrassed the church in recent months.

The archbishop of Atlanta, Eugene A. Marino, resigned in July following revelations of a two-year "intimate relationship" with a young woman. In Newfoundland, Canada, a report in July by a church-appointed commission said priests had sexually abused boys in the province for more than a decade.

"Some priests question this requirement (celibacy), and some candidates leave formation for this reason," the working document said.

It noted that in public opinion, celibacy is "often incomprehensible and ridiculed." A priest who accepts celibacy "is sometimes looked upon in a strange way," it said.

"In this situation a priest can become totally isolated and misunderstood to the point of becoming deeply demoralized," it said. "In some cases, the crisis in the priestly identity can explain why priests leave the ministry."

The Vatican cited "the phenomenon of burnout, from which priests of all ages seem to suffer. They live in situations marked by tiredness, resignation, lack of creativity."

The document lamented the shortage of priests and declining number of candidates in some countries.

According to the latest statistics, there are 400,000 priests in the world, down from 406,000 five years ago.